1. Field of the Invention
This invention relates to a metal plane support for making multi-layer lead frames adapted to be used for semiconductor devices. This invention also relates to a process for manufacturing multi-layer lead frames using such a metal plane support.
2. Related Art
As shown in FIG. 9, a conventionally known multi-layer lead frame comprises a lead frame 2 and at least one metal plane, such as a power-supply plane 3, a ground plane 4, and the like, laminated by means of electrically insulating layers 5a and 5b made of suitable resin material, such as polyimide or the like. These electrically insulating layers 5 (5a and 5b) serve for electrically insulating the respective layers, i.e., the lead frame 2, the power-supply plane 3 and the ground plane 4 and also to adhere the respective layers together thereby to form a unitary multi-layer lead frame.
Although the multi-layer lead frame shown in FIG. 9 has a structure of three layers, such a multi-layer lead frame may be a two-layer structure comprising a single metal plane, i.e., a power-supply plane or a ground plane. Moreover, such a multi-layer lead frame may be a structure having four or more layers.
The power supply plane 3 and the ground plane 4 are electrically connected to power-supply leads and ground leads of the lead frame 2, respectively, and therefore maintained at predetermined voltages, respectively. In order to attain this, the power-supply plane 3 and the ground plane 4 have extensions 6 and 7 protruding outwardly from predetermined positions of the outer peripheries thereof. Thus, after the power-supply plane 3, the ground plane 4 and the lead frame 2 are laminated together by means of electrically insulating layers 5a and 5b, these extensions 6 and 7 are electrically connected to the power supply leads and the ground leads of the lead frame 2, respectively, by spot welding, laser beam welding, or the like.
Although FIG. 9 shows an example in which the second, intermediate layer is a power-supply plane 3 and the lowermost layer is a ground plane 4, a multi-layer lead frame in which the second layer is a ground plane and the lowermost layer is a power-supply plane is also known in the prior art.
When manufacturing a multi-layer lead frame by laminating the power supply plane and the ground plane onto the lead frame, as mentioned above, the power-supply plane and the ground plane must be accurately positioned with respect to the lead frame. Also, these layers must be firmly adhered to each other while remaining insulated, and a reliable and effective manufacturing method must be attained.